Transmission system



Marchso, 1943; l

v F. A. LEIBE TRANSMISSION SYSTEM .W h T KURSE www vwww ma ow March 30, 1943.

F. A. I EIBEl TRANSMISSION SYSTEM 2 Sheets-Sheet Filed my 9, 1940 E14. LE/BE A 7` TOR/VE V Patented Mar. 30, 1943 TRANSMISSION SYSTEM Frank A. Leibe, Quakertown, Pa., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 9, 1940, Serial No. 344,515

2 Claims.

This invention relates to transmission systems and more particularly to transmission systems involving unattended repeater stations.

An object of the invention is to facilitate supervision of a transmission system which involves unattended repeater stations.

A more specinc object of the invention is to indicate at an attended repeater station the condition of unattended repeater stations of the transmission system.

It is customary in modern transmission systems, -particularly those involving a large number of signal channels such as a coaxial cable system, to provide a large number of line repeaters in tandem spaced at intervals which may be as short as live miles or even less, with several unattended repeater stations between attended stations; a section between two attended stations may be from fifty to one hundred miles in length. While repeater equipment is now available which is sufficiently reliable in its operation to justify this practice of leaving the majority of the stations normally unattended, the possibility of an occasional failure can never be entirely ruled out. It is desirable, therefore, that means be provided at the attended stations whereby the operating condition of the unattended repeater stations to be supervised therefrom may be readily determined whenever desired without interrupting the normal use of the transmission system.

In accordance With a specific embodiment of the invention, a narrow band-pass filter is provided at each unattended repeater station being connected across the west-east and the east-West lines. These filters are normally maintained in disabled condition, i. e., in condition wherein resistance to passage of current is high. In order to test the condition of an unattended repeater station a pilot frequency is applied to the westeast line at the West attended station and the filter associated with the repeater station to be tested is enabled, i. e., placed in condition to readily pass current of frequency included within its pass band. If the West-east line amplifier and the east-West line amplifier of the station under test be fully operative and assuming that the intervening stations are known to be operative, the pilot current will pass through the west-east line amplifier, will be shunted through the filter to the other line, will pass through the east-west line amplifier and will return to the attended station where an indicator will be operated. Failure of the pilot current to return or return of the current in greatly attenuated condition will indicate that either line amplifier at the station under test is not operating satisfactorily.

A feature of the invention is means whereby the lters of a plurality of unattended repeater stations may be selectively enabled from an attended station.

Full understanding of the arrangements contemplated by the present invention and appreciation of the valuable features thereof will be gained from consideration of the following detailed description in connection with the drawings, in which:

Figs. 1 and 3 illustrate schematically a twoway transmission system including features of Vthe present invention; and

Figs. 2 and 4 illustrate schematically a system similar to that of Figs. 1 and 3, a specific form of enabling means being shown. During consideration of the drawings, Figs. 1 and 3 should be joined, left and right respectively, and Figs. 2 and 4 should be likewise joined.

Referring now to Figs. 1 and 3, there is illustrated schematically a two-way transmission system joining attended repeater station A-I (west) and attended repeater station A-Z (east).

The system utilizes two lines, which may, for example, be coaxial cable lines, line II being the west-east line and line I2 the east-West line. The portion of the system illustrated in Figs. 1 and 3 may conveniently be referred to as a section, attended stations A-I and A-Z being the control stations for the section.

A West-east line amplifier and an east-West line amplifier are provided at each unattended repeater station, the west-east ampliners being designated as I3, I4, I5, I6, II, 2|, 22, 23, 24

and 25 and the east-west amplifiers being designated as 26, 27, 4|, 42, 43, 44, 45, 4t, 41 and 5I. A band-pass filter is also provided at each unattended repeater station, these filters being connected between lines II and I2. The filters are designated 54, 55, 56, 51, 1I, 12, 13, I4, 1'5 and 'I6 respectively. Suitable enabling means are provided for each of these filters, the enabling devices being designated as 8|, 82, 83, 84, 85, 85, 8l, IOI, |02 and |03 respectively.

In the section illustrated, unattended repeater stations U-I to U-IL inclusive, are arranged for control from attended repeater station A-|, e

andunattended repeater stations U-5 to U-ID, inclusive, are arranged for control from attended repeater station A-Z. Means, designated as |04, for controlling enabling devices 8| to 84, inclusive, are provided at station A-I and means,

designated as It, for controlling the remaining enabling devices are provided at station A-Z. The band-pass filters of those stations arranged for control from station A-I are connected across the output of the respective west-east amplifier and the input of the respective eastwest amplifier while the band-pass filters of those stations arranged for control from station A-2 are connected across the output of the respective east-west amplifier and the input of the respective west-east amplifier.

Source III provided at station A-I supplies a wave of special pilot frequency f1 to west-east line Il when connected thereto by switch I I2; source IIS provided at station A-Z supplies a wave of the same pilot frequency to east-west line I2 when connected thereto by switch IM. While it is desirable in order to obtain uniformity of equipment design that pilot current of the same frequency be supplied by both sources III and I I3, it will be apparent, of course, that so far as the operating principies of the circuit are concerned two different pilot frequencies may be utilized. In such event, the lters would be modified accordingly with respect to the band of frequencies passed. A suitable pilot indicator I I5, which is arranged to respond only to current of frequency f1 and which may comprise a filter and voltmeter, is provided at station A-I and may be connected to line i2 by switch IE6; a similar indicator I II is provided at station A--2 and may be connected to line I I by switch ISI.

In order to describe the arrangement further, let us assume first that We wish to test line amplifiers I3 and 2G of unattended repeater station T T-I. This unattended station is included in the group controlled from station A-.I. Control means Ill is first operated to cause energization of enabling device 8l thereby enabling bandpass, filter Eli which is arranged to. pass only a narrow band of frequencies, the frequency f1 being included. Switch II2 is operated thereby connecting the pilot frequency f1 to line Il and switch It is operated thereby connecting pilot indicator II to line I2.

Now, assuming that both line amplifiers of station UI are operating properly, the pilot wave of frequency fr applied tor line II will pass through amplifier I3, band-.pass filter 55, (this being the only band-pass filter in enabled condiu tion), amplifier 2d and back over line I2 to station A where indicator IE5 will be. operated. Should either amplifier I3 or 2li. be inoperative the pilot frequency will not, of course, be returned over line I2, which fact will be indicated by non-operation of indicator H5; should either amplifier be operating at an efficiency substantially below itsY normal value, the pilot frequency will be returned with greater than normal attenuation, which fact will be indicated by operation of indicator H5 to some point below the normal operate point.

Should failure of either line amplifier I3 or 2E be. indicated, the respective one at fault may be found by restoring filter E@ to disabled condition and connecting indicator II'I of station A-2 to line II. and source IIS to line I2 respectively, indicator IIfii-fand source III remaining connected to lines i2 and I I as before. The condition of amplifier I3 will then, of course, be shown by operation or non-operation of indicator Hl and the condition of amplifier 26 by operation or non-operation of' indicator H5.

The line amplifiers of unattended repeater stations U-2, lil- .3 and UL-I may be tested in a manner similar to that described above, the associated filter being enabled through controlling means III-i. The amplifiers of unattended stations U5 to U-I, inclusive, are tested in a similar manner but under control of apparatus located at attended station A-L That is, source I I3 and indicator I I 'I are utilized and the control of the enabling devices is exercised by means H35.

The enabling devices and the selective controlling means may take various forms including various selectively operated relay arrangements, variable inductance coils utilizing ferromagnetic cores and the like. One specific arrangement utilizing polarized relays is illustrated in Figs. 2 and 4 and will now be described in detail.

Referring now to Figs. 2 and 4, the system disclosed is similar to that of Figs. l and 3, attended repeater stations A--l (west) and A-4 (east) being connected by west-east line le and east-west line tdt?. Unattended repeater stations U-il to U-Iig inclusive, are arranged for control from station A- and unattended repeater stations U-.I to U-, inclusive, are arranged for control from station .Fr-ii. A west-east line amplifier and an east-west line amplifier are provided at each unattended station, the westeast amplifiers being designated M3 to |41, inclusive, and III to |65, inclusive, and the east- West amplifiers being designated as Ii, Il, III to I'I'I, inclusive, and IQI.

A band-pass filter is provided at each unattended repeater staticn, being connected across lines IflI and lili. These filters are designated i972` to IE'I, inclusive, and 2iII to, 2&4, inclusive. An enabling device, comprising in certain instances a single polarized relay and in other instances a pair of such relays, is associated with each filter, these relaysV being designated Ziii' to 2M, inclusive, 22I to 22?, inclusive, and V232 and 232. Stations U-II tov U-M, inclusive, are arranged to be controlled from station A-3 and the enabling devices of these stations are selectively controlled over lines 233. and 23.14 by means provided at. station A-f-i; stations U-I5 to U-20, inclusive, are arranged to be controlled from station A-l and the enabling devices of those stations are selectively controlled over lines 235 and 23d by means. provided at station And.

Source 25| provided at station A.-3 supplies a Wave of special pilot frequency f1 to line IliI when connected thereto. by switch 2&2 a similar source 253; at station A--fi supplies a wave of the same pilot frequency to line U12 when connected thereto by switch 25%.'. A suitable pilot indicator 255 is provided at station A--S and a similar indicator 25.5 is provided at station A-f., connection of these indicators toy lines M2 and IM being controlled by operation of switches 25.? and 258, respectively.

Suitable. sources of potential for control of enabling relays 205, 2%, ZIIl and 22| are provided at station A-d, the selective application 'of these potentials to lines 2.3.3- and 234 being controlled byoperation. of switch 261 to contacts 2%2- and 25.3 and by operation of switch 264 to contacts and' 255 Similarly, suitablepotential sources for control of the. remaining enabling relays are provided at station A.4, the selective application of these potentials to lines 235 and 236. being controlled by operation of switch. 261 to contacts 28I and 282, switch 2.813 to contacts 2.84; and 28.5., and switch 28.6,to contacts 28T and 291;..

In order tov further illustrate the. operation of the4 system, let u s assume. that line amplifiers 443 and |66 of unattended repeater station U--II that of U--l1 -just described except Vfor the lfact are to be tested from attended station A. The general testing scheme is the same as that described above in reference to Figs. 1 and 3 and willlnot be described here; the specific enabling arrangement will be described in detail however.

In order to test the line amplifiers of station U-I I, band-pass` filter |92 must, of course, be enabled As represented schematically in the drawings, the output of filter |92 is connected to line |42 through the make contact of relay 2 05 so that with relay 205 unoperated, as shown, lter |92 offers infinitely high impedance to passage of current. With relay 205 in operated position, however, the output path to line |42 is completed at the make contact of the relay and lter |92 will pass a narow band of frequencies which includes the special pilot frequency f1. The arrangement is preferably such that the loss through filter |92 in enabled condition is substantially such with regard to the normal loss in the line that the pilot level returning to the point of measurement will be approximately the f same as the outgoing pilot level. In order to operate relay 205, thereby enabling filter |92, switch 26| is moved to contact 263 thereby completing an operating circuit for relay 205 traced from positive side of battery 29|, switch 26 contact 263, line 233, operating winding of relay 205 and back to the negative side of battery 29|.

The enabling relays are adapted to operate only on current in the respective directions indicated by the arrows so that relay 201 does not operate at this time even though its operating winding is also connected to line 233. In order to cause operation 'of relay 201, should it be desired to test the line amplifiers of station U|3', switch 264 is moved to contact 265 thereby completing an operating circuit for relay 201 traced from positive side of battery 292 to ground, operating winding of relay 201, line 233, contact 265, switch 264 to negative side of battery 292.

. Relays 206 and 22| are operated in a manner similar to that described by operation of switch 26| to contact 262 and switch 264 to contact 266, respectively.

Considering now the unattended repeater stations controlled from attended station A-4, here we have a slightly more involved layout as six stations are included in this group rather than four as in the group controlled from station A-3. Relays 23| of station U|9 and 232 of station U-20 are the same as those referred to above and are operated in a manner similar to that previously described by operation of switch 286 to contact 281 and operation of the same switch to contact 29|, respectively.

Now at station U|1 We have two relays connected in series, relay 224 which is of the type heretofore described and relay 225 which is designed to operate only on current of a Value substantially higher than that which will operate relay 224 and the other relays heretofore described. In order to enable filter 20| of station U-|1, switch 283 is moved to contact 284 thereby completing an operating path for relay 224 traced from positive side of battery 295, switch 283, contact 284, line 235, winding of relay 224, winding of relay 225 to ground and back to the negative side of the battery. Relay 224 operates over this path and closes its make contact to enable filter 20| relay 225 does not operate, however, as the current'ilowing is not sufficient to operate this high-current relay.

The arrangement at station U-IB is similar to that the relay windings are connected to line 236 -instead of line 235. In order to enable lter 202, therefore, switch-283 is moved to contact 285 instead of 283.

Operation of high-current relay 222 in order to enable lter |96 of station U|5 is caused by `moving switch 261 to contact 28| lthereby bringing batteries 295 and 296 both into play over a path traced from positive side of battery 296, switch 261, Contact 28|, line 235, winding of relay 222, to ground and back to the negative side of battery 295. Relay 222 operates over this path and closes its make contact to enable filter |96. While relay 224 is also operated over this path, filter 20| is not enabled in view of the fact that the current flow is suiiicient at this time to operate relay 225 also thereby opening the enabling path cf the lter at the break contact of the last-mentioned relay.

The arrangement of station U-I 6 is similar to that of station U-I5 except for the fact that the relay winding is connected to line 236 instead of line 235 so that operation of high-current relay 223 necessary to enable lter |91 is accomplished by operating switch 261 to contact 282 rather than contact 28|. While relay 226 is also operated over this path, filter 202 is not enabled due to operation at the same time of relay 221.

While certain specific embodiments of the invention have been selected for detailed description, the invention is not, of course, limited in its application to those embodiments described. The embodiments described should be taken as illustrative of the invention and not as restrictive thereof.

What is claimed is:

1. In a signaling system comprising an attendedstation and a plurality of unattended repeater stations geographically separated from the attended station and from each other and having an east transmission line joining the attended station and the unattended stations for speech transmission in one direction and a west transmission line joiningthe attended station and the unattended stations for speech transmission in the opposite direction, means at the attended station for applying a testing current to the east line, a frequency selective path at each of the unattended stations joining when enabled the east line and the west line, the frequency of the testing current being within the band of frequencies passed by the frequency selective paths, means for normally disabling said frequency selective paths and means at the attended station for selectively enabling said frequency selective paths one at a time for transmission of the testing current from the east line to the West line.

2. In a signaling system comprising an attended station and a plurality of unattended repeater stations geographically separated from the attended station and from each other and having a west transmission line joining the attended station and the unattended stations for transmission in one direction and an east transmission line joining the attended station and the unattended stations for transmission in the opposite direction in which each unattended station includes a pair of line amplifiers, one amplii'ler of each pair being in series with the west transmission line and the other amplier of each pair being in series with the east transmission line, a band-pass lter at each of the unattended stations connected when enabled across the output of one of the amplifiers of a respective pair and they input of the other amplier of the same respectivepair, said band-pass filters normally being in disabled condition and offering an excessively high resistance to passage of current,

,means at said attended station for applying a testing current to one of said lines, the frequency of said testing current being that passed by said .bandpass filters when enabled, a normally open .enabling circuit for each of said band-pass filters, i0

f4 aangaat 'a relay connected in each of said enabling cir- FRANK A. LEIBE. 

